| Hi all , | | We are trying to implement the micro-BGA technology at our plant. I need the clarification to the following points: | | 1. Is underfill required for micro-BGAs? | | 2. What type of stencil apertures are the industry standards for uBGAs and of what size and thickness.? | | Thanks and regards | Upinder | ====== | Upinder,

Underfill is not needed, depending on the application (aerospace with harsh environments as continuous thermal and mechanical shock) and part density. We are doing .5mm without it. Our .8mm devices use .017" pads with a stencil aperture about .020" round in 6 mil thick stencil foils.

I am still working on optimizing .5mm uBGA requirements though 4-5 mil stencil thicknesses (stepped down as needed from 6 mils) with nearly 1:1 aperture to pad ratios look good as little shorting at X-Ray is apparent using nearly standard reflow profiles as for most BGA types.

We experience little rework. When needed, we use micro stencils to print paste for .8mm types. With those below, we use a syringe method to apply paste (see Blankenhorn's stuff).

I'm a late starter in .5mm types. Where is Justin when you need him? I think he was doing this stuff over a year ago and probably has lots of reliabillity data I've not yet developed.

I'm looking for 500 to 1,500 T/M cycles to failure using dummies with TDR testing not exceeding 300 ohms - hopefully less. Also looking at X-Sections with certain failures.

| | Hi all , | | | | We are trying to implement the micro-BGA technology at our plant. I need the clarification to the following points: | | | | 1. Is underfill required for micro-BGAs? | | | | 2. What type of stencil apertures are the industry standards for uBGAs and of what size and thickness.? | | | | Thanks and regards | | Upinder | | ====== | | | Upinder, | | Underfill is not needed, depending on the application (aerospace with harsh environments as continuous thermal and mechanical shock) and part density. We are doing .5mm without it. Our .8mm devices use .017" pads with a stencil aperture about .020" round in 6 mil thick stencil foils. | | I am still working on optimizing .5mm uBGA requirements though 4-5 mil stencil thicknesses (stepped down as needed from 6 mils) with nearly 1:1 aperture to pad ratios look good as little shorting at X-Ray is apparent using nearly standard reflow profiles as for most BGA types. | | We experience little rework. When needed, we use micro stencils to print paste for .8mm types. With those below, we use a syringe method to apply paste (see Blankenhorn's stuff). | | I'm a late starter in .5mm types. Where is Justin when you need him? I think he was doing this stuff over a year ago and probably has lots of reliabillity data I've not yet developed. | | I'm looking for 500 to 1,500 T/M cycles to failure using dummies with TDR testing not exceeding 300 ohms - hopefully less. Also looking at X-Sections with certain failures. | | Earl Moon | Thanks for the reply, Earl.

I was going thru some literature of teh US Robotics guys and they sugggest to use square apertures equal to the pad size for uBGAs. Any pointer or suggestion on that?

| | | Hi all , | | | | | | We are trying to implement the micro-BGA technology at our plant. I need the clarification to the following points: | | | | | | 1. Is underfill required for micro-BGAs? | | | | | | 2. What type of stencil apertures are the industry standards for uBGAs and of what size and thickness.? | | | | | | Thanks and regards | | | Upinder | | | ====== | | | | | Upinder, | | | | Underfill is not needed, depending on the application (aerospace with harsh environments as continuous thermal and mechanical shock) and part density. We are doing .5mm without it. Our .8mm devices use .017" pads with a stencil aperture about .020" round in 6 mil thick stencil foils. | | | | I am still working on optimizing .5mm uBGA requirements though 4-5 mil stencil thicknesses (stepped down as needed from 6 mils) with nearly 1:1 aperture to pad ratios look good as little shorting at X-Ray is apparent using nearly standard reflow profiles as for most BGA types. | | | | We experience little rework. When needed, we use micro stencils to print paste for .8mm types. With those below, we use a syringe method to apply paste (see Blankenhorn's stuff). | | | | I'm a late starter in .5mm types. Where is Justin when you need him? I think he was doing this stuff over a year ago and probably has lots of reliabillity data I've not yet developed. | | | | I'm looking for 500 to 1,500 T/M cycles to failure using dummies with TDR testing not exceeding 300 ohms - hopefully less. Also looking at X-Sections with certain failures. | | | | Earl Moon | | | Thanks for the reply, Earl. | | I was going thru some literature of teh US Robotics guys and they sugggest to use square apertures equal to the pad size for uBGAs. Any pointer or suggestion on that? | | Regards | Upinder | ====== | Upinder,

Our R&D group (pretty extensive and experienced) has not recommended anything square. However, many others do use square apertures. Therefore, I cannot comment but for what seems to be working based on someone elses (the folks in R&D) input. I must, at this time, abide by this but really am going to do more testing and analysis. Maybe the folks at Tessera can be of service as Vern Solberg or Joe Felstad.

| | | | Hi all , | | | | | | | | We are trying to implement the micro-BGA technology at our plant. I need the clarification to the following points: | | | | | | | | 1. Is underfill required for micro-BGAs? | | | | | | | | 2. What type of stencil apertures are the industry standards for uBGAs and of what size and thickness.? | | | | | | | | Thanks and regards | | | | Upinder | | | | ====== | | | | | | | Upinder, | | | | | | Underfill is not needed, depending on the application (aerospace with harsh environments as continuous thermal and mechanical shock) and part density. We are doing .5mm without it. Our .8mm devices use .017" pads with a stencil aperture about .020" round in 6 mil thick stencil foils. | | | | | | I am still working on optimizing .5mm uBGA requirements though 4-5 mil stencil thicknesses (stepped down as needed from 6 mils) with nearly 1:1 aperture to pad ratios look good as little shorting at X-Ray is apparent using nearly standard reflow profiles as for most BGA types. | | | | | | We experience little rework. When needed, we use micro stencils to print paste for .8mm types. With those below, we use a syringe method to apply paste (see Blankenhorn's stuff). | | | | | | I'm a late starter in .5mm types. Where is Justin when you need him? I think he was doing this stuff over a year ago and probably has lots of reliabillity data I've not yet developed. | | | | | | I'm looking for 500 to 1,500 T/M cycles to failure using dummies with TDR testing not exceeding 300 ohms - hopefully less. Also looking at X-Sections with certain failures. | | | | | | Earl Moon | | | | | Thanks for the reply, Earl. | | | | I was going thru some literature of teh US Robotics guys and they sugggest to use square apertures equal to the pad size for uBGAs. Any pointer or suggestion on that? | | | | Regards | | Upinder | | ====== | | | Upinder, | | Our R&D group (pretty extensive and experienced) has not recommended anything square. However, many others do use square apertures. Therefore, I cannot comment but for what seems to be working based on someone elses (the folks in R&D) input. I must, at this time, abide by this but really am going to do more testing and analysis. Maybe the folks at Tessera can be of service as Vern Solberg or Joe Felstad. | | Keep us posted as will I you all, | | Earl Moon | I've had printing problems in the past with uBGAs using round apertures which resulted in insufficent solder paste on the pad. When I switched to square pads this defect was greatly reduced; with my solder paste, printer, print parameters, etc. Worked for me...

| | | Hi all , | | | | | | We are trying to implement the micro-BGA technology at our plant. I need the clarification to the following points: | | | | | | 1. Is underfill required for micro-BGAs? | | | | | | 2. What type of stencil apertures are the industry standards for uBGAs and of what size and thickness.? | | | | | | Thanks and regards | | | Upinder | | | ====== | | | | | Upinder, | | | | Underfill is not needed, depending on the application (aerospace with harsh environments as continuous thermal and mechanical shock) and part density. We are doing .5mm without it. Our .8mm devices use .017" pads with a stencil aperture about .020" round in 6 mil thick stencil foils. | | | | I am still working on optimizing .5mm uBGA requirements though 4-5 mil stencil thicknesses (stepped down as needed from 6 mils) with nearly 1:1 aperture to pad ratios look good as little shorting at X-Ray is apparent using nearly standard reflow profiles as for most BGA types. | | | | We experience little rework. When needed, we use micro stencils to print paste for .8mm types. With those below, we use a syringe method to apply paste (see Blankenhorn's stuff). | | | | I'm a late starter in .5mm types. Where is Justin when you need him? I think he was doing this stuff over a year ago and probably has lots of reliabillity data I've not yet developed. | | | | I'm looking for 500 to 1,500 T/M cycles to failure using dummies with TDR testing not exceeding 300 ohms - hopefully less. Also looking at X-Sections with certain failures. | | | | Earl Moon | | | Thanks for the reply, Earl. | | I was going thru some literature of teh US Robotics guys and they sugggest to use square apertures equal to the pad size for uBGAs. Any pointer or suggestion on that? | | Regards | Upinder | ====== | Using square apertures has pros and cons. The pro of the sqaure aperture is it distorts the shape of the solder joint, making Xray inspection much easier. You will readily see when you are at the proper depth ad inspecting the joints. The con to square pads can be routing. The square pad will cut down on the routing channels and can increase the layers or force you to additive layer processing. This will depend uopon the pitch. If you opt to use the square pad then try to match the pad width on the bottom of the package and do not get fooled by matching to the ball diameter. Usually a rule of thumb that works well is the pad should be 50% of the pitch. Jim